When an impact on a vehicle, which is caused by a crash or overturn of the vehicle running at not lower than a predetermined speed, is detected by an impact detecting sensor, an airbag is inflated and developed so as to protect a driver and passenger(s).
Generally, a fabric for an airbag comprises, in addition to a textile substrate, a coating layer to enhance the air-tightness of the fabric.
While a polyamide yarn such as nylon 66 yarn was mainly used for preparing the textile substrate, a polyester yarn for an airbag, which can replace the polyamide yarn, is under research and developments these days in order to satisfy the needs of cost reduction.
The textile substrate may be a woven fabric of plain weave pattern or basket weave pattern, or a woven fabric of OPW (One Piece Woven) type. The woven fabric is prepared by interlacing warp and weft threads in various manners. For example, according to a plain weaving method, the warp threads alternately and periodically ascend and descend between relatively high and relatively low positions, thereby forming spaces, and the weft threads are inserted in the spaces in a direction substantially perpendicular to the warp threads.
The warp threads for the weaving process may be prepared by sequentially performing a warping process, sizing process, beaming process, drawing-in process, etc. In the warping process, the warp threads unwound from a creel are arranged based on the designed warp density and width, and the designed length of the warp threads are wound on a warper beam. In the beaming process, a plurality of warp threads provided from a warper beam are put together in accordance with the warp number of the designed fabric and are wound on a loom beam. In the sizing process performed right before the warp threads are wound on the loom beam, a sizing agent is applied to the warp threads in order to improve their bundling and weaving properties. In the drawing-in process, the warp threads wound on the loom beam are mounted on dropper, heald, and reed. A weaving process for interlacing the as-prepared warp threads with weft threads is carried out to complete a woven fabric.
The sizing agent conventionally used in the sizing process to improve the weavability of the woven fabric for an airbag is an acryl-based sizing agent. Since the acryl-based sizing agent has worse adhesive strength to a polyester yarn compared to its adhesive strength to a polyamide yarn, however, a problem of its separation from the polyester yarn during the weaving process occurs.
Once the weaving process is completed, the sizing agent adhered to the yarn functions as an impurity, thereby decreasing the peel strength between the textile substrate and coating layer and increasing the stiffness of the airbag fabric as well. Particularly, since an airbag mounted in a vehicle is maintained in an enclosed space for a long time until an accident occurs, the adhesive strength between the textile substrate and coating layer is likely to further deteriorate, thereby increasing the risk that the coating layer will easily peel off from the textile substrate when the airbag is developed by an inflator.